Drilling fluids or muds (hereinafter collectively referred to as "drilling muds") are an important part of well-drilling operations, performing a variety of functions that influence the drilling rate, and the cost, efficiency, and safety of the operation. In general, the drilling mud is pumped down a hollow drill string, and returns to the surface through the annular space between the hole or casing and the exterior of the drill string. According to conventional methods, the drilling mud after reaching the surface is passed through a series of screens, shale shakers which remove coarse cuttings coated with the mud and fluids, settling tanks or similar equipment to remove formation material called "cuttings" brought to the surface. The mud is then reconstituted and pumped back into the well and the cycle repeated.
Drilling muds are generally composed of liquids containing suspended, finely divided solids of various types. Commonly used liquids are water, diesel crude oil, mineral oil or a mixture of these, and the solids include high-density solids such as hematite (Fe.sub.2 O.sub.3) and barite (BaSO.sub.4), clays such as bentonite, attapulgite, sepiolite, and organophilic clays (prepared for example from bentonite or attapulgite and aliphatic amine salts), and polymers such as guar and xanthan gums, cellulose derivatives, and polyacrylamides, the drilling mud must be disposed of. In the current practice, water-based muds are either buried or discharged at sea. Oil and diesel-based muds, however, cannot be disposed of in this manner and thus present an environmental problem. Used drilling muds recovered from drilling operations in oil-bearing formations are particularly troublesome due to their high content of crude oil from the formations themselves. Since the only dump sites suitable for these muds are Class I dump sites, and they cannot be discharged at sea, these muds are commonly held in tanks or open pits. As an indication of the volume of these materials produced from a typical drilled well, a 10,000 foot well will result in the following:
cuttings: 8030 cu. ft., or approximately 810,810 pounds PA1 fluid volume (mud) discharged: 5349 bbl or 224,658 gal PA1 solids (dry weight, assuming 15% solids content of mud): 33,700 pounds
Clearly there is a growing need for approved disposal facilities and sites.
An additional disposal problem arises from the inclusion of soluble salts in drilling muds. These soluble salts are used for increasing the density of the mud among other reasons, as a means of balancing formation pressures. Examples are potassium chloride, sodium chloride, sodium carbonate, calcium chloride, potassium carbonate, sodium bromide, calcium bromide, zinc chloride and zinc bromide. These salts must be removed prior to land disposal of the spent drilling mud.